The present invention relates to an improvement of a copying machine equipped with an automatic document feeder by which a document is automatically supplied onto the exposed surface, and particularly to a copying machine equipped with an automatic document feeder by which timing of document feeding, exposure scanning, and recording sheet feeding is automatically adjusted, and controlled so that copying productivity is efficiently increased.
The automatic document feeder for the copying machine (which will be called ADF, hereinafter) is an apparatus by which a document set in a document tray is automatically conveyed to a platen, and the document is delivered on a delivered sheet tray after the document has been copied by the copying machine. This apparatus is suitable for high speed copying of documents having many pages.
Recently, in copying machines, the following is required in order to increase the copying property high speed copying is required in order to increase the number of copied sheets per minute; a high document conveyance speed of the ADF (about 1000 to 1200 mm/sec) is required; and the times for document exchange, such as setting the document in a predetermined exposed position and delivering the document therefrom, are reduced so that the number of processed original sheets per minute (OPM) is increased.
Generally, in copying machines with ADF, there are the following methods by which a document is fed to a predetermined position on the platen glass provided on the upper surface of the copying machine and stopped thereon.
(1) An end of the document is contacted with a document positioning stopper provided on one side of the platen glass, and the document is stopped. In this method, there are the following problems: collision noises are generated when the document is contacted with the stopper; a means to prevent the document from going over a positioning plate is necessary; ends of the document are sometimes damaged; productivity is low because the document is switched back or conveyed at low speed when the document is contacted with the document positioning plate; and when a movable stopper is used for reversal conveyance of a two-sided document, the structure is complicated.
(2) In a method by which the document is stopped at a predetermined position on the platen glass by controlling a motor, without using the document positioning plate when the ADF is operated, for example, an encoder is directly coupled with the motor, and an operator stops the motor by an electromagnetic brake while monitoring a signal generated by the encoder. In this case, there are problems in which: a strong electromagnetic brake is necessary; the structure of the apparatus is complicated; and noises are generated when the magnetic brake is operated.
These are document stopping methods in the automatic document feeder(ADF). In the recording sheet feeding of the copying machine, the recording sheet supply is started in timed relation with an optical travelling system of an exposure scanning means, which is unconnected with the ADF control.
Therefore, the timing of the document conveyance by ADF is not matched with the recording sheet supply in the copying machine. In order to prevent a time lag of the image on the recording sheet, sufficient time is necessary when the document is exchanged, and therefore copying productivity, that is, a ratio of OPM (the number of original sheets conveyed per minute in ADF) and CPM(the number of sheets copied per minute in the copying machine) is lowered.
As a document feeding control apparatus, techniques in Japanese Patent Publication No. 59308/1987, Japanese Patent Publication Open to Public Inspection No. 79820/1977, and Japanese Utility Model Open to Public Inspection No. 31550/1980 have been disclosed. However, these techniques relate to document stopping control in ADF, or document jamming detection.